The typical asking rate per listing is in the $20's per square foot per year. The National City submarket is going through a a rise in rates. In the last 3 months, the median rate rose $25 per sqft per year. That's a Inf% increase in rent.
Compared to the rest of the San Diego market, the National City submarket has less expensive rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 14 listings have come on the market, which means new listings might be leasing quickly. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 830 sqft. Most properties in this market are around 3 floors. Most buildings in this market were built in 1974 and are Class B.